1. Field of the Invention
The present invention relates to an image forming device such as printer, facsimile device or copier, which utilizes electrophotography, and a recording medium storing a program used in such image forming device.
2. Description of the Related Art
In a conventional printer using electrophotography, a photoconductor is exposed based upon image data and a latent image is formed. For exposure, a laser unit that irradiates a laser beam is often used. The above laser unit is acquired by integrating a laser and an optical system for focusing a laser beam from the laser on the photoconductor. For example, the laser unit is constructed by a laser diode array or by another laser unit having a polygon mirror for scanning a laser beam from a laser radiating apparatus.
The laser unit has to be mounted on the printer so that a scanning direction of the laser beam generated from the laser unit is in parallel to a main scanning direction of the photo-conductor. But, when the laser unit is mounted on the printer with the scanning direction thereof being in not parallel to the main scanning direction of the photo-conductor, it is impossible to generate a correct image data on the photoconductor.
FIG. 1 shows a case that a laser unit is installed in a condition such that the laser beam skews in a right-handed upward direction with respect to a horizontal scanning direction of a photoconductor. The arrows L100 to L600 show a laser scanning direction in which image data is output. Assuming that a scanning width in a horizontal direction (main scanning direction) X is X0, and a right-hand upward direction with respect to the horizontal direction X is a positive skew direction and a right-hand downward direction with respect to the horizontal direction is a negative skew direction. In this case, FIG. 1 shows that image data is output on printing paper with the image data skewed by xe2x80x98+5xe2x80x99 lines within the main scanning width X0. If the laser unit is mounted on the printer with the scanning direction thereof being in parallel to the main scanning direction X of the photo-conductor, as shown in line I-2 in FIG. 1, the image data is not skewed.
However, in the above example of the conventional type, the larger the quantity of skew is, the worse the quality of printing of an output result becomes. Therefore, it can be said that the degree of skew has an effect upon the performance of a printer. Also, when a laser unit is installed, it is required to be precisely assembled to reduce the quantity of skew. Therefore, a problem that the manpower of the assembly is remarkably increased, a fixture and others are required to be produced and the price of a printer rises occurs.
An object of the present invention is to provide a method for correcting an image data with high precision.
Another object of the present invention is to provide a recording medium storing a program for executing a procedure of dividing lines of an image data to blocks.
In order to achieve the above objects, an image forming device according to the present invention has a recording unit which records an image data line by line while scanning a recording medium with a laser; a memory circuit for storing the image data corresponding to a plurality of lines of the image data; an operation circuit for dividing the image data stored in the memory circuit per line into blocks and generating an image data block having the number of pixels corresponding to an amount of skew with respect to a main scan line direction of the laser from the recording unit; and a control circuit for selecting pixel data from the image data block in corresponding two blocks of the adjacent two lines and combining the image data block and the selected pixel data to produce a line data to be supplied to the recording unit.
A scan speed of the recording unit in the main scan line direction may be made twice that of a usual scan speed or a relative scan speed of the recording unit to the recording medium in a sub scan line direction may be made a half that of a usual case when the skew is not generated.
The recording unit may be a laser beam irradiation device and the recording medium may be a photo-conductor scanned by a laser beam from the recording unit.
The image forming device may further has a measuring unit for measuring the amount of tilting.
Further, a recording medium according to the present invention stores a program for executing a procedure of; dividing an image data stored in a memory circuit per line into blocks and generating an image data block having the number of pixels corresponding to an amount of skew with respect to a main scan line direction of a recording unit; selecting pixel data from the image data block in corresponding two blocks of the adjacent two lines; and combining the image data block and the pixel data to produce a line data to be supplied to the recording unit.
The program may include a sub program for executing a procedure of making a scan speed of the recording unit in the main scan direction twice that of a usual case when the skew is not generated.
The program may include a sub program for executing a procedure of making a relative speed of the recording unit and the recording medium in a sub scan direction a half of that of a usual case.
The program may include a sub program for executing a procedure of measuring a tilting amount of the recording unit in the main scan direction.